This invention relates to computer and electronic components and, more particularly, to sound card circuit configurations and related components for generating or processing audio signals.
Sound cards are add-on boards that are employed within a personal computer or related device to produce or process audio signals to enhance sound quality, or for enabling sound capabilities, of the computer. Sound cards may, for example, produce or enhance a signal representing sounds corresponding to a prompt or like sound from an ordinary computer program, sounds for video games played on the computer, and downloadable music or sounds such as, for example, in an MPEG Audio Layer standard. Conventional sound cards may also be capable of capturing and processing signals from musical instruments.
The circuitry of a conventional sound card may include audio subsystems for digital audio capture and replay and music synthesis, including by an internal FM synthesizer and by playing a digitized or sampled sound. A matched pair of digital-to-analogue (DAC) and analogue-to-digital (ADC) converters coupled with a programmable sample rate generator may be provided to process digital audio.
In addition to an interface with the computer bus, sound cards typically provide an interface to a player that is capable of playing music and/or video, such as compact discs and digital video disks, which will be referred to herein as CD-ROMS. They also support proprietary interfaces for the CD-ROM player, as well as standard interfaces such as SCSI and IDE/EIDE and like standards. Thus, a sound card may process signals from CD-ROMS or other play-back equipment, downloaded or stored files (including telephone answering machine files), musical instruments, and the like.
Several connectors may be part of a sound card to provide digital or analog connections thereto. Such connectors include one or more microphone-in connector, line-in and line-out connector, loudspeaker-out connector, musical instrument digital interface (“midi”) port, joystick port, cd audio-in or similar connector, auxiliary-in connector, telephone answering device in connector, digital out connector, optical or coaxial digital I/O card connector, headphone out connector, and the like.
Some of the connectors may be accessible from outside of the computer. Specifically, the headphone connector or headphone jack typically protrudes through or is accessible through an aperture in the sound card bracket, which encloses the expansion slot. The sound card circuitry may be configured such that the audio signal to the loudspeaker output connector(s) is muted in response to inserting a headphone plug into the headphone connector. In such a configuration, in which the audio signal is audible through loudspeakers electrically connected to the loudspeaker output connector, plugging the headphone plug into the headphone connector mutes the sound emitted from the loudspeakers in favor of providing the audio signal to the headphones.
Some computer manufacturers have placed a headphone jack (or a microphone jack) at a location that is convenient to the user, such as the computer front panel. To connect it to the audio signal, the front headphone jack may be connected to the sound card. Merely connecting the front headphone jack in parallel with the rear headphone jack would make it difficult or impossible to mute the audio signal in response to insertion of the front headphone connector into the front headphone jack while retaining the auto-mute function of the primary headphone connector. On the other hand, connecting the front headphone jack to a normally-open front connector on the sound card in series with the rear headphone connector has the disadvantage that the signal must be transmitted to the front of the computer and back to the sound card, even during operation with the rear headphone jack or the loudspeakers. Further, because not all computer manufacturers employ a front headphone jack in addition to the rear headphone jack, sound card manufacturers must produce two versions of the same sound card, and computer manufacturers and sound card re-sellers and retailers would be required keep two versions of each sound card in stock—one conventional sound card for use with computers employing only a single (that is, rear) headphone jack and another for use with computers employing both a rear and front headphone connector.